Bonded medium

ABSTRACT

Thermally shock stable bonded solid materials are formed by mixing a solid mineral or inorganic material in an aqueous medium with a lignosulfonate, treating the aqueous medium with a metal ion- based complexing agent (such as lime), with application of heat sufficient to maintain the lignosulfonate in fluid form, so as to produce an intimate mix of saturated slaked lime with lignosulfonate and the mineral or inorganic material, and thoroughly mixing the resulting substantially dry material with dry urea (or a derivative thereof) so as to cause the mix to agglomerate, preferably followed by shaping the agglomerates by briquetting or the like.

BACKGROUND OF THE INVENTION

The present invention is concerned with bonded media. Certain inorganicmaterials are sometimes present in a form in which they are difficult tohandle and use. For example, basic oxygen steelmaking sludge (which is awaste product from the basic oxygen steelmaking process), contains up to30% moisture and solids, including ferrous sulfide, iron oxide andvarious foundry additives, as well as other metals such as zinc.

Basic oxygen steelmaking sludge is generally considered to be a wasteproduct, for which disposal is very expensive and difficult, partlybecause of its zinc content. We have now devised a way of using suchbasic oxygen steelmaking sludge, and other mineral and inorganicmaterials.

According to the present invention therefore, there is provided a methodof forming thermally shock stable bonded solid materials, whichcomprises mixing a solid mineral or inorganic material in an aqueousmedium with a lignosulfonate, treating the aqueous medium with apolyvalent or polydentate cationic complexing agent for lignosulfonate,with application of heat sufficient to maintain said lignosulfonate influid form, so as to produce an intimate mix of said complexing agentwith said lignosulfonate and said mineral or inorganic material, andthoroughly mixing the resulting substantially dry material with asubstantially dry further reagent comprising urea or a urea derivative,so as to cause the mix to agglomerate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The resulting agglomerates can be shaped into, for example, briquettes(formed between shaped dies or the like) or pellets, or similar bodiesformed by extrusion, pan agglomeration or the like.

The lignosulfonate may be used in method according to the invention inthe form of a solution (such as an aqueous solution). Alternatively,when the mineral or organic material is itself aqueous, thelignosulfonate may be used in powder form. The lignosulfonate mayinclude any suitable cation(s); examples of suitable cations areammonium, calcium, magnesium, sodium or potassium. Of these, calcium ismost preferred.

The cationic complexing agent may comprise a transition metal or analkaline earth metal; the metal is preferably of the fourth period ofthe Periodic Table of the elements, such as calcium, iron or the like.Of these, calcium is preferred, preferably in the form of the oxide(preferably as lime, which has the advantage of reacting with any freewater in the mix).

When lime is used, it is preferably added to the aqueous medium in suchan amount as to produce a saturated slaked mix, having a pH typically inexcess of 10.

The further reagent is preferably added in powdered form and mixed withthe saturated slaked mix by contra-rotating blade mixing or by tumbling,until the mix becomes plastic; this mixing may be carried out at atemperature ranging from ambient to up to about 80° C. The furtherreagent is preferably urea or a urea derivative (such as an alkyl urea).

When the mineral or inorganic material treated by the method accordingto the invention is basic oxygen steelmaking sludge, then the resultingshaped agglomerates can undergo direct reduction to a ferrous metalsource, for addition to molten steel or iron in a steelmaking process.The direct reduction with carbon as reducing agent, which is typicallycarried out at about 900-1000° C., is advantageously withoutdisintegration of the agglomerates because of their highly advantageousthermal shock resistance. Any zinc, furthermore, may be volatilised offfrom the shaped agglomerates during the direct reduction phase.

It is a particular advantage of the present invention, when applied tothe process of forming agglomerates from basic oxygen steelmaking sludgeor other inorganic or mineral materials, that highly thermalshock-resistant agglomerates can be formed. Such agglomerates aresubstantially dry and can be added to high temperature direct reductionprocesses or the like without any deleterious water evolution (whichcould otherwise have potentially devastating, explosive consequences).It is believed that this thermal shock resistance is beneficiallyassociated with the formation of sulfonyl and sulfur bridges between thepolymeric (lignin-based) backbones. Calcium sulfate formed in theslaking step is also believed to beneficially contribute to such thermalshock resistance. The sulfur present in the resulting agglomerates isstoichiometrically bonded in such a form that disadvantageous evolutionof oxides of sulfur, or other noxious sulfur compounds, is substantiallyprecluded.

The present invention will now be further illustrated, by way of exampleonly, in the following Examples.

EXAMPLE 1

100 grams of basic oxygen steelmaking sludge, which contained 30% byweight of water, was partially dried, to a solids content of about 12%by weight. 10 grams of calcium lignosulfonate was added as a dry powder,with stirring. Lime (calcium oxide) was then added incrementally, so asto be slaked by the water present in the mix, resulting in a dry powder(the amount of lime being about 5 grams).

3 grams of powdered urea were then added and the mix was tumbledtogether at a temperature of about 60° C., so as to produce anagglomerated mass. The resulting mass (which had a pH in excess of 10)was formed into briquettes between shaped dies.

The resulting briquettes were highly stable to thermal shock, and couldbe added in the form of briquettes to a direct reduction process, asreferred to above without disintegration.

EXAMPLE 2

200 grams of ferrous sulfide was supplied to a Bekin double-bladecontra-rotating mixer; 20 grams of an aqueous solution of calciumlignosulfonate containing 50% by weight of water, was added to obtain afairly wet mix.

10 grams of lime (calcium oxide) was then added incrementally, so as tobe slaked by the water present in the mix, and the plastic mix wasthereby converted to a free-flowing powder.

5 grams of powdered urea were then added and the mix was blended, so asto result in a volume increase in the mixer, and an increase in thepower input to the mixer (from 65 to 95 watts), the resulting mix beingplastic. The resulting mass (which had a pH of about 12) was formed intobriquettes in a single floating ring die.

The resulting briquettes were highly stable to thermal shock, and couldbe added directly to molten ferrous sulfide, without disintegration. (Ina test, thirty of the briquettes were thrown into molten ferroussulfide; none broke and the briquettes floated and gradually melted inthe ferrous sulfide.

I claim:
 1. A method of forming thermally shock stable bonded solidmaterials, which comprises mixing a solid mineral or inorganic materialin an aqueous medium with a lignosulfonate, then, after the mixing step,treating the aqueous medium with a polyvalent or polydentate cationiccomplexing agent for lignosulfonate, with application of heat sufficientto maintain said lignosulfonate in fluid form, so as to produce anintimate mix of said complexing agent with said lignosulfonate and saidmineral or inorganic material, and then, after the treating step,thoroughly mixing the result substantially dry material with asubstantially dry further reagent comprising urea or a urea derivative,so as to cause the mix to agglomerate.
 2. A method according to claim 1,wherein the lignosulfonate is in the form of an aqueous solution.
 3. Amethod according to claim 1, wherein the complexing reagentlignosulfonate is in the form of a calcium salt.
 4. A method accordingto claim 1, wherein the complexing agent comprises a transition metal oran alkaline earth metal.
 5. A method according to claim 3, wherein themetal is of the fourth period of the Periodic Table of the elements. 6.A method according to claim 1, wherein the complexing agent comprises acalcium compound.
 7. A method according to claim 6, wherein the calciumcompound is the oxide.
 8. A method according to claim 1, wherein thefurther reagent comprises urea.
 9. A method according to claim 8,wherein the urea is added in powdered form and mixed with the saturatedslaked mix by tumbling or by means of contra-rotating blades, until themix becomes plastic.
 10. A method according to claim 9, wherein themixing is carried out at a temperature in the range from ambient toabout 80° C.
 11. A method according to claim 1, which further comprisesshaping the agglomerates into briquettes, pellets or extruded bodies.12. A method according to claim 1, wherein the mineral or inorganicmaterial comprises basic oxygen steelmaking sludge.
 13. A methodaccording to claim 12, wherein the shaped agglomerates are added tomolten steel or iron in a steelmaking process.
 14. A method according toclaim 1, wherein the mineral or inorganic material comprises ferroussulfide.